1. Field of the Invention
The present invention relates to a timing device, namely a timing ruler or a timing disk for the exact positioning of working machines, servo-motors, encoders or the like, consisting of a transparent material on which codings are arranged for scanning via optical sensors; as well as to a process for its manufacture.
2. The Prior Art
Timing rulers or timing disks of the type specified above are known from DE 295 04 883 U1. As a rule, the timing disks are secured on a rotating axle, for example of an encoder. A beam of light generates pulses by the transmitted-light method when the disk is rotating. The light source is disposed in this connection parallel with the axis of rotation and transmits a beam of light onto the disk at a right angle.
The sequence xe2x80x9cpermeable to light/impermeable to lightxe2x80x9d preset on the coded timing disk produces on the rotating disk xe2x80x9cwindowxe2x80x9d openings of a defined width and length, which are used for generating pulses. The beam of light exiting from a light source (emitter) is converted by a receiver (optical sensor) disposed in the optical axis of the beam of light into a pulse, whereby the accuracy of the pulse is dependent upon the quality of the xe2x80x9cwindowsxe2x80x9d.
The timing disks or timing rulers mentioned above have been successfully applied in practical life. However, in certain application cases, for example in a moist atmosphere or at temperatures above 100xc2x0 C., problems sometimes arise, because the film may delaminate and/or soften under such circumstances, so that the accuracy of the measurement suffers.
On the other hand, timing disks or timing rulers have been manufactured from glass, metal, or thermally stable plastic. However, such timing disks are costly both on the material side and with respect to the manufacturing process, and, furthermore, do not offer the required accuracy which, for example, is part of the standard preconditions that need to be satisfied in the field of application of encoders.
Therefore, the problem of the present invention is to further develop a timing disk or timing ruler of the type specified above in such a way that such timing disks or rulers can be employed without limitations also in a moist atmosphere and in particular at temperatures in excess of 100xc2x0 C. The goal in this connection is also to dispense with the use of expensive materials and to make the manufacturing process suitable for mass production operations with an output of more than 100,000 units per day.
This problem is solved by the timing device and process for its manufacture according to the invention. It has now been found that by covering the exposed and developed film material with a foil and by selectively sealing the edges, it is possible to produce a timing ruler/timing disk which is thermally stable and resistant to moisture under the aforementioned conditions. The film material serving as the base of the timing ruler/timing disk is a standard film material with a photolayer preferably having a reflecting coating on one side. After the transmitter and the receiver, i.e. the light source and the optical sensor have been combined in one chip, the components can be arranged as an assembly on one side of the timing ruler or timing disk. Scatter and diffraction of the light rays can be reduced and phenomena of interference can be avoided owing to the low layer thicknesses.
Both the metal layer and the transparent light-sensitive layer are preferably coated with a protective layer. Such a protective layer may consist of a foil laminated to the element, such a foil made of plastic, for example polypropylene or polyethylene. The stability of the timing disk is substantially enhanced by such a protective layer.
The edges of the timing ruler or timing disk are advantageously sealed. This is explained in the following in greater detail with the help of a number of exemplified embodiments.